An automatic guidance by voice (audio) is practically used in a navigation device, an elevator, a vehicle, an automated teller machine, or the like. Voice guidance is set to a predetermined voice volume, so that senior people having weak hearing or hearing-impaired people cannot easily hear the voice guidance. Technologies to solve this problem are described in Patent Documents 1, 2.                Patent Document 1: JP-H6-1549 A        Patent Document 2: JP-2002-229581 A        
In Patent Document 1, a voice guidance device functions as follows: An individual recognition means is installed in a cage or a platform of an elevator for recognizing a passenger; broadcast data corresponding to hearing-impaired people is read out from a broadcast data storing means by a broadcast command; and a voice corresponding to the broadcast command is outputted from a speaker.
In Patent Document 2, a voice output system includes the following: a voice output device for outputting voices; a voice converting device for converting frequencies, tempos, accents, voice volumes, provincialisms, etc. of the outputted voices; and a voice recognition degree analyzing device for analyzing users' recognition degrees with respect to the outputted voices or their contents.
The above individual recognition means in Patent Document 1 requires a large memory volume and an intelligent search system when the number of target people significantly increases. The above voice recognition degree analyzing device in Patent Document 2 is very complicated system that needs to retrieve data such as user information, vehicle states, environment information, etc. and to compare present data with data in standard states with respect to the retrieved data to thereby compute users' recognition degrees.